Lobed drive for hi-lite fastener

ABSTRACT

A drive socket for a male threaded fastener includes three rounded lobes of equal radius which are located equidistant from the center of the fastener and 120° apart from each other. The drive socket also includes three flat surfaces, each flat surface being located opposite one of the lobes and equidistant from the center of the fastener. Another embodiment of a drive socket includes a first set of three lobes and a second set of three lobes, each lobe being of equal radius and equidistant from the center of the fastener. The lobes of the first set are 120° apart and the lobes of the second set are also 120° apart and 60° apart from the lobes of the first set. Each of the lobes of the first set includes a flat surface which is adjacent and tangential to the radius portion of the lobe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 10/052,238, filed Jan.16, 2002, now U.S. Pat. No. 6,655,888.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to structural fasteners, and moreparticularly relates to drive sockets on threaded male structuralfasteners.

2. Description of Related Art

Threaded male structural fasteners of the type to which this inventionis directed include an axial drive socket, or wrench engaging recess,located either on a head (FIG. 1 a) of the fastener or on the oppositeend of the fastener (FIG. 1 b). The drive socket (FIG. 1 c) includes aplurality of substantially equally spaced and sized flat surfaces whichreceive a mating wrench type key, or wrench key. The drive socket may behexagonally shaped to receive a hexagonal Allen wrench type key, orhex-key driver. During use, an end of the wrench key is inserted intothe drive socket in the male fastener and is either held in place topermit a threaded female fastener, such as a nut, to be screwed onto thethreads of the male fastener, or the hex-key driver is rotated in orderto screw the male fastener into the female fastener or other femalethreaded hole.

Clearance is required between a hex-key driver and the drive socketwhich the hex-key driver is inserted into. For example, the clearancebetween a 2.4 mm ( 3/32-inch) hexagonal drive socket and a 2.4 mm (3/32-inch) hex-key driver is 0.04 mm (0.0015 inch) all around. With thisamount of clearance, the hex-key driver can rotate approximately threedegrees before contacting the mating surfaces of the drive socket (FIG.1 d), resulting in the intersections, or corners, between the surfacesof the hex-key driver contacting the flat surfaces of the drive socket.With the corners between the surfaces of the hex-key driver providingthe main driving force from the hex-key driver, high stressconcentrations are placed on the corners of the hex-key driver, butthere is very little material providing support for the corners. As aresult, when a load that is sufficient to set the desired torque betweenthe male threaded fastener and the female threaded fastener or part isapplied to a hex-key driver during use, the material at the corners mayshear off of the hex-key driver, leaving the hex-key driver in astripped condition.

Another problem that can occur is that as the hex-key driver is rotatedwithin the drive socket, the hex-key driver may become wedged within thesocket, thus causing the hex-key driver to bind within the socket. Aftersetting the desired torque between the male threaded fastener and thefemale threaded fastener, rotation of the hex-key driver must bereversed to break the bind between the hex-key driver and the socket.

Methods which have been developed to prevent the stripping of hex-keydrivers during use include fabricating the hex-key drivers from strongermaterials. The present invention reduces the need for a specialhigh-strength hex-key. Another method of preventing hex-key drivers fromstripping includes making the drive sockets in the fasteners deeper.However, making the drive socket deeper may compromise the tensilestrength of the fastener through the area of the drive socket,especially on fasteners having the drive socket on the end of thefastener opposite the head (FIG. 1 b).

One attempt to alleviate the problem of the hex-key drivers strippingwithin the drive sockets included reconfiguring the drive socket toinclude six rounded lobes of substantially equal radius, as depicted inFIG. 2 a. The lobes are located substantially equidistant from thecenter of the fastener. Also, adjacent lobes are located substantiallyequidistant circumferentially from each other. Each of the lobesprojects inward toward the center of the fastener. The embodiment alsoincludes six curved recesses located between and adjacent each lobe,thereby combining for a total of six recesses. Each of the recesses isblended into its adjacent lobes to form a substantially smoothtransition between the lobes and the recesses.

Referring to FIG. 2 b, when the hex-key driver is rotated, such as todrive the male threaded fastener relative to a female threaded fastener,a portion of the flats on the hex-key driver contact the lobes while thecorners of the hex-key driver remain within the recesses and out ofcontact with the wall of the drive socket. One problem with theconfiguration of FIGS. 2 a and 2 b is that it enlarges the drive socketconsiderably, thereby weakening the fastener head.

Hence, those skilled in the art have recognized a need for a malethreaded fastener having a drive socket that may receive high stressfrom a hex-key driver and reduce the tendency of the hex-key driver tostrip or to bind within the drive socket. The need to configure thedrive socket so that it substantially maintains the tensile strength ofmale threaded fasteners and the strength of the fastener head has alsobeen recognized. The present invention fulfills these needs and others.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the present invention is directed to adrive socket for a fastener which is driven by a hex-key driver. In onepresently preferred embodiment, the drive socket includes three roundedlobes of substantially equal radius. The three lobes are positionedabout a center of the fastener and are located substantially equidistantfrom the center and approximately 120° apart from each other. The drivesocket also includes three flat surfaces positioned about the center ofthe fastener. Each flat surface is located substantially opposite one ofthe lobes and substantially equidistant from the center of the fastener.The drive socket further includes recesses which are located between thelobes and the flat surfaces.

In one currently preferred aspect of the invention, the lobes projectinward toward the center of the fastener. Each of the recesses forms asubstantially smooth transition between a lobe and a flat surface. Thelobes are positioned to provide a first clearance between an apex ofeach of the lobes and corresponding surfaces on a hex-key driverinserted into the drive socket. The flat surfaces are positioned toprovide a second clearance between the flat surfaces and correspondingsurfaces on the hex-key driver. In one currently preferred embodiment,the first clearance is approximately 0.04 mm (0.0015 inch) and thesecond clearance is approximately 0.10 mm (0.0038 inch). In anothercurrently preferred embodiment, the recesses are sized to providesufficient clearance such that the corners of a hex-key driver insertedinto the drive socket do not contact a wall of the drive socket.

In another presently preferred embodiment, the drive socket of thepresent invention includes a first set of three lobes of substantiallyequal radius which are positioned about a center of the fastener. Thelobes within the first set are substantially equidistant from the centerof the fastener and approximately 120° apart from each other. Each ofthe lobes of the first set includes a flat surface which is locatedadjacent and substantially tangential to the radius portion of the lobe.The drive socket also includes a second set of three lobes ofsubstantially equal radius positioned about the center of the fastener.The lobes within the second set are substantially equidistant from thecenter of the fastener, approximately 120° apart from each other andapproximately 60° apart from the lobes of the first set. The drivesocket further includes recesses located between the lobes of the firstset and the lobes of the second set.

In one currently preferred aspect of the invention, each of the lobes ofthe first set and each of the lobes of the second set projects inwardtoward the center of the fastener. In another currently preferred aspectof the invention, the radius of the lobes of the first set and theradius of the lobes of the second set are substantially equal. Thedistance between the lobes of the first set and the center of thefastener and the distance between the lobes of the second set and thecenter of the fastener are also substantially equal. Each of therecesses forms a substantially smooth transition between the lobes ofthe first set and the lobes of the second set. The recesses are sized toprovide sufficient clearance such that the corners of a hex-key driverinserted into the drive socket do not contact a wall of the drivesocket. The flat surfaces of the lobes in the first set are positionedsubstantially 120° apart from each other.

In another currently preferred aspect of the invention, the lobes of thefirst set are positioned to provide a first clearance between an apex ofeach of the lobes of the first set and corresponding surfaces on ahex-key driver inserted into the drive socket. Similarly, the lobes ofthe second set are positioned to provide a second clearance between anapex of each of the lobes of the second set and corresponding surfaceson the hex-key driver inserted into the drive socket. The firstclearance and the second clearance are both approximately 0.04 mm(0.0015 inch).

From the above, it may be seen that the present invention provides forconfigurations of drive sockets for fasteners which reduce the tendencyof the hex-key driver to strip or to bind within the drive socket.Further, it may also be seen that the drive socket substantiallymaintains the tensile strength of the fastener and the strength of thefastener head. These and other aspects and advantages of the inventionwill become apparent from the following detailed description and theaccompanying drawings, which illustrate by way of example the featuresof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is section view of an embodiment of a prior art fastenerdepicting a hexagon shape drive socket positioned at the head of thefastener.

FIG. 1 b is a section view of an embodiment of a prior art fastenerdepicting a hexagon shape drive socket positioned at an end of thefastener opposite the head.

FIG. 1 c is a plan view of the drive socket of FIG. 1 b depicting thedrive socket with a hex-key driver inserted within the drive socket.

FIG. 1 d is a plan view of the drive socket of FIG. 1 c with the hex-keydriver rotated within the drive socket.

FIG. 2 a is a plan view of the head of a prior art fastener depicting adrive socket having six lobes and six recesses with a hex-key driverinserted within the drive socket.

FIG. 2 b is a plan view of the head of FIG. 3 a with the hex-key driverrotated within the drive socket.

FIG. 3 a is a plan view of a drive socket having three lobes and threeflat surfaces with a hex-key driver inserted within the drive socket.

FIG. 3 b is a plan view of the drive socket of FIG. 3 a with the hex-keydriver rotated within the drive socket.

FIG. 4 a is a plan view of a drive socket having six lobes with three ofthe lobes including a flat surface with a hex-key driver inserted withinthe drive socket.

FIG. 4 b is a plan view of the drive socket of FIG. 4 a with the hex-keydriver rotated within the drive socket.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the drawings for purposes of illustration, the invention isembodied in a drive socket for a male threaded fastener. Referring tothe drawings, in which like reference numerals are used to designatelike or corresponding elements among the several figures, FIG. 3 adepicts a drive socket 20 of the present invention. The drive socket 20includes three rounded lobes 22 of substantially equal radius. The lobes22 are located substantially equidistant from the center 24 of thefastener 26, as well as substantially equidistant circumferentially fromeach other. Each of the lobes 22 projects inward toward the center 24 ofthe fastener 26. The drive socket 20 may also include three flatsurfaces 28, each flat surface being located substantially opposite oneof the lobes 22 and substantially equidistant from the center 24 of thefastener 26.

The drive socket 20 of one currently preferred embodiment may alsoinclude curved recesses 30 between the lobes 22 and the flat surfaces28, thereby combining for a total of six recesses. Each of the recesses30 may be blended into its adjacent lobe 22 and flat surface 28 to forma substantially smooth transition between the recesses and the lobes andbetween the recesses and the flat surfaces.

The lobes 22, flat surfaces 28 and recesses 30 of the drive socket 20are spaced from the center 24 of the fastener 26 such that when ahex-key driver 32 is inserted into the drive socket, there is a firstclearance 34 between an apex 36 of each of the lobes and a first set ofalternating flat surfaces 38 on the hex-key driver. In one currentlypreferred embodiment, the first clearance 34 is approximately 0.04 mm(0.0015 inch). A second clearance 40 is also provided between the flatsurfaces 28 of the drive socket 20 and a second set of alternating flatsurfaces 42 on the hex-key driver 32. In one currently preferredembodiment, the second clearance 40 is approximately 0.10 mm (0.0038inch). Also, the recesses 30 provide sufficient clearance such that thecorners 44 of the hex-key driver 32 do not contact the wall 46 of thedrive socket 20.

Referring to FIG. 3 b, when the hex-key driver 32 is rotated clockwise,such as to drive the male threaded fastener 26 relative to a femalethreaded fastener, a portion of each of the flat surfaces of the firstset of alternating flat surfaces 38 on the hex-key driver contacts thelobes 22 in the drive socket 20 while the corners 44 of the hex-keydriver remain out of contact with the wall 46 of the drive socket. Thecorners 44 of the hex-key driver 32 may either remain within therecesses 30 or move to a location proximate the flat surfaces 28 of thedrive socket 20. In one currently preferred embodiment, the hex-keydriver 32 may rotate approximately 6° prior to contact between the firstset of alternating flat surfaces 38 on the hex-key driver and the lobes22 with the lobes contacting the first set of alternating flat surfaceson the hex-key driver approximately one-third of the distance across thesurfaces from the corners 44 of the hex-key driver. As a result, arelatively large amount of material supports the hex-key driver 32behind the three contact points between the hex-key driver and the lobes22 in comparison to the prior art hexagonal drive socket (FIGS. 1 c and1 d).

Counterclockwise rotation of the hex-key driver 32 (not shown), such asto unscrew the male threaded fastener 26, creates substantiallyequivalent contact between the drive socket 20 and the hex-key driver aswhen the hex-key driver is rotated clockwise. Hence, a portion of eachof the flat surfaces of the first set of alternating flat surfaces 38 onthe hex-key driver contacts the lobes 22 in the drive socket 20 whilethe corners 44 of the hex-key driver remain out of contact with the wall46 of the drive socket. Contact between the lobes 22 and the first setof alternating flat surfaces 38 occurs approximately one-third of thedistance across the surfaces from the corners 44 of the hex-key driver32.

By eliminating contact between the corners 44 of the hex-key driver 32and the wall 46 of the drive socket 20, as depicted in FIGS. 3 a and 3b, wear to the hex-key driver is significantly reduced in comparison tothe use of the prior art drive socket of FIG. 1 c. Due to the reductionof wear to the hex-key driver 32 by the configuration of the drivesocket 20, the depth of the drive socket may be reduced in comparison tothe prior art drive socket. Further, the inclusion of the flat surfaces28 reduces the amount of material removed from the fastener 26 incomparison to the prior art drive socket depicted in FIGS. 2 a and 2 b.Reducing the amount of material removed from the fastener 26 aids inmaximizing the strength of the fastener 26.

Referring to FIG. 4 a, another currently preferred embodiment of a drivesocket 50 includes a first set of three lobes 52 and a second set ofthree lobes 54, for a total of six lobes, each lobe being ofsubstantially equal radius. The lobes 52, 54 are located substantiallyequidistant from the center 56 of the fastener 58. The lobes 52 of thefirst set are approximately 120° apart from each other. The lobes 54 ofthe second set are also approximately 120° apart from each other andalternate between the lobes 52 of the first set so that each lobe 52from the first set is approximately 60° apart from a lobe 54 of thesecond set. Each of the lobes 52, 54 projects inward toward the center56 of the fastener 58. Each of the lobes 52 within the first setincludes a flat surface 60 which is located adjacent and substantiallytangential to the radius portion 62 of the lobe 52. The flat surfaces 60are positioned such that they are substantially 120° apart from eachother. The flat surfaces 60 on the lobes 52 of the first set and thelobes 54 of the second set function as contact surfaces for a hex-keydriver 64 during clockwise rotation of the fastener.

The drive socket 50 of the present invention may also include a firstset of curved recesses 66 and a second set of curved recesses 68 betweenthe lobes 52 of the first set and the lobes 54 of the second set,thereby combining for a total of six recesses. However, the first set ofrecesses 66, which are located between the flat surfaces 60 on the lobes52 of the first set and the adjacent lobes 54 of the second set may be adifferent size than the second set of recesses 68 which are locatedbetween the radius portions 62 of the lobes 52 of the first set and theadjacent lobes 54 of the second set. Each of the first 66 and second 68sets of recesses may be blended into the first 52 and second 54 sets oflobes to form a substantially smooth transition between the recesses andlobes.

The first 52 and second 54 sets of lobes and first 66 and second 68 setsof recesses of the drive socket 50 are spaced from the center 56 of thefastener 58 such that when the hex-key driver 64 is inserted into thedrive socket 50, there is a clearance 70 between the hex-key driver andthe drive socket. More particularly, there is a clearance 70 between afirst apex 72 on each of the lobes 52 of the first set and a first setof alternating flat surfaces 74 on the hex-key driver. There is asubstantially equal clearance 70 between a second apex 76 on each of thelobes 54 of the second set and a second set of alternating flat surfaces78 on the hex-key driver. In one currently preferred embodiment, theclearance 70 is approximately 0.04 mm (0.0015 inch). Also, the first 66and second 68 sets of recesses provide sufficient clearance such thatthe corners 80 of the hex-key driver 64 do not contact the wall 82 ofthe drive socket 50.

Referring to FIG. 4 b, when the hex-key driver 64 is rotated clockwise,such as to drive the male threaded fastener 58 relative to a femalethreaded fastener, the first set of alternating flat surfaces 74 on thehex-key driver contact the flat surfaces 60 of the first set of lobes 52in such manner that there is substantially surface-to-surface contactbetween the first set of alternating flat surfaces on the hex-key driverand the flat surfaces of the first set of lobes. Further, the second setof alternating flat surfaces 78 on the hex-key driver 64 contacts thethree lobes 54 of the second set. The corners 80 of the hex-key driver64, however, remain within the first 66 and second 68 set of recessesand out of contact with the wall 82 of the drive socket 50. In onecurrently preferred embodiment, the hex-key driver 64 may rotateapproximately 6° prior to contact between the first 74 and second 78sets of alternating flat surfaces on the hex-key driver and the first 52and second 54 set of lobes of the drive socket 50. In this manner, theflat surfaces 60 of the first set of lobes 52 may have surface contactwith the surfaces of the first set of alternating flat surfaces 74 onthe hex-key driver 64 between the corner 80 of the hex-key driver to alocation approximately one-third of the distance across the surfaces ofthe first set of alternating flat surfaces. Also, the lobes 54 of thesecond set may contact the surfaces of the second set of alternatingflat surfaces 78 at a location approximately one-third of the distanceacross the surfaces of the second set of alternating flat surfaces fromthe corners 80 of the hex-key driver. As a result, similar to the use ofthe drive socket 20 in the embodiment depicted in FIGS. 3 a and 3 b, arelatively large amount of material supports the hex-key driver 64behind the contact points and contact surfaces in comparison to theprior art hexagonal drive socket (FIGS. 1 c and 1 d).

With the surface contact created between the flat surfaces 60 of thefirst set of lobes 52 and the first set of alternating flat surfaces 74of the hex-key driver 64 during clockwise rotation of the hex-keydriver, the likelihood of the hex-key driver binding is significantlyreduced in comparison to the prior art drive sockets (FIG. 1 c). Withthe reduction of binding of the hex-key driver 64 within the drivesocket 50, there is less need to reverse the rotation direction of thehex-key driver to break the bind prior to removing the hex-key driverfrom the drive socket. Further, the reduction of binding reduces theamount of wear to the hex-key driver 64 during use.

When the hex-key driver 64 is rotated counterclockwise (not shown), suchas to unscrew the male threaded fastener 58, each of the first 74 andsecond 78 set of alternating flat surfaces on the hex-key driver 64 maycontact a corresponding lobe from the first 52 or second 54 set of lobeswhile the corners 80 of the hex-key driver, again, remain within thefirst 66 and second 68 sets of recesses and out of contact with the wall82 of the drive socket 50. The lobes 52, 54 of the first and second setcontact the first 74 and second 78 sets of alternating flat surfaces onthe hex-key driver 64 approximately one-third of the distance across thesurfaces from the corners 80 of the hex-key driver.

By eliminating contact between the corners 80 of the hex-key driver 64and the wall 82 of the drive socket 50, as depicted in FIGS. 4 a and 4b, wear to the hex-key driver is significantly reduced in comparison tothe prior art drive socket of FIG. 1 c. Due to the reduction of wear ofthe hex-key driver 64 by the configuration of the drive socket 50, thedepth of the drive socket may be reduced in comparison to the prior artdrive socket. Reducing the depth of the drive socket 50, in turn, aidsin maximizing the strength of the fastener 58.

It will be apparent from the foregoing that while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

1. In a fastener having a drive socket for receiving a key driver havinga plurality of flat surfaces and a plurality of corners at intersectionsbetween the plurality of flat surfaces, the improvement comprising: thedrive socket having a surface defining a plurality of rounded lobes ofsubstantially equal radius located substantially equidistant from acenter of the fastener and substantially equidistant circumferentiallyfrom each other, the plurality of rounded lobes receiving a set ofalternating ones of said plurality of flat surfaces of the key driver;the drive socket having a corresponding plurality of flat surfaces, eachflat surface being located substantially opposite one of the roundedlobes and substantially equidistant from the center of the fastener, andthe plurality of corners of the key driver remaining out of contact withsaid plurality of flat surfaces; and the drive socket surface definingcurved recesses smoothly transitioning between the rounded lobes and theflat surfaces, and the plurality of corners of the key driver remainingout of contact with said curved recesses.
 2. The fastener of claim 1,wherein each of the rounded lobes projects inward toward the center ofthe fastener.
 3. The fastener of claim 1, wherein the rounded lobes arepositioned to provide a first clearance between an apex of each of therounded lobes and corresponding surfaces on a key driver inserted intothe drive socket, and the flat surfaces are positioned to provide asecond clearance between the flat surfaces and corresponding surfaces onthe key driver.
 4. The fastener of claim 3, wherein: the first clearanceis approximately 0.04 mm (0.0015 inch); and the second clearance isapproximately 0.10 mm (0.0038 inch).